Thermal and abrasion resistant sintered alloy

ABSTRACT

An alloy prepared by molding a powdery composition comprising 0.6 to 2 percent of carbon, 0.5 to 5 percent of molybdenum, 6 to 15 percent of cobalt and 1 to 5 percent of copper, by weight, and the balance being iron, and then sintering the molded composition has large thermal resistance and abrasion resistance.

States Patent Takahashi et al.

[ Feb. 26, 1974 THERMAL AND ABRASION RESISTANT SINTERED ALLOY Inventors: Kentaro Takahashi, Ohmiya;

Minoru Hasegawa, Saitama; Kaoru Nara, Kawaguchi, all of Japan Assignee: Nippon Piston Ring Co., Ltd.,

Tokyo, Japan Filed: Sept. 5, 1972 Appl. No.: 286,389

Foreign Application Priority Data Sept. 2, 1971 Japan 46/66979 US. Cl. 29/182 75/123 J, 75/123 K, 75/126 l-l, 75/126 A, 75/126 C, 75/128 B, 75/128 D, 75/128 W, 75/200, 191/59.l

Int. Cl. B22f 1/00, B22f 5/00 Field of Search 19l/59.1; 29/1821, 182; 75/200, 123 J, 123 K, 126 H, 126 A, 126 C, 128 B, 128 D, 128 W Primary ExaminerCarl D. Quarforth Assistant Examiner-B. Hunt Attorney, Agent, or FirmSughrue, Rothwell, Mion, Zinn & Macpeak [5 7] ABSTRACT An alloy prepared by molding a powdery composition comprising 0.6 to 2 percent of carbon, 0.5 to 5 percent of molybdenum, 6 to 15 percent of cobalt and 1 to 5 percent of copper, by weight, and the balance being iron, and then sintering the molded composition has large thermal resistance and abrasion resistance.

1 Claim, 2 Drawing Figures THERMAL AND ABRASION RESISTANT SINTERED ALLOY BACKGROUND OF THE INVENTION A publicly known metal such as chromium, cobalt, tungsten, etc. has not only a large abrasion resistance but also is prominent in its characteristics at elevated temperatures and is applied in various fields. However, such a metal has many problems to be solved when it is used as sintered parts for a machine. That is, such a metal has high melting point so that the sintering temperature is, of necessity, required to be elevated and the sintering time has to be extended, and, therefore, it is naturally disadvantageous in cost.

SUMMARY OF THE INVENTION The present invention provides a sintered alloy having large thermal resistance and abrasion resistance suitable for use as a sliding element such as, for example, a valve sheet in which high thermal resistance and high abrasion resistance are required. That is, the present invention comprises a sintered thermal and abrasion resistant alloy comprising a molded and sintered powdery composition consisting of by weight 0.6 to 2 percent of carbon, 0.5 to 5 percent of molybdenum, 6.0 to percent of cobalt, l to 5 percent of copper and the balance iron.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the abrasion resistance of sintered alloys of the Examples and of a conventional cast iron and sintered iron when evaluated in a valve sheet abrasion test machine; and

FIG. 2 is a graph showing the hardness at elevated temperatures of sintered alloys of the Examples and of a conventional cast iron and a sintered iron alloy.

DETAILED DESCRIPTION OF THE INVENTION In the sintered alloy of the present invention, carbon is solidified in an iron base to form a fine pearlite structure and plays a large role in improving the strength of the alloy material, however, when the carbon content is less than 0.6 percent, by weight, the alloy changes to a ferrite structure which decreases the hardness necessary for abrasion resistance, while, with more than 2.0 percent of carbon, the alloy changes to a cementiteexcessive structure which becomes unnecessarily high in hardness and increases in brittleness.

Molybdenum increases the tenacity of the alloy as well as the impact strength and endurance limit, and, on the other hand, improves the heat treatment property and stabilizes the structure after sintering to contribute to the thermal and abrasion resistance of the alloy. However, little effect is obtained if less than 0.5 percent of molybdenum is present and with more than 5 percent no increased effect corresponding to the increase level is obtained.

Copper promotes the liquid sintering to strengthen the base structure, however, the effect is small with less than 1 percent of copper and, when the amount of copper exceeds 5 percent, it has the action of forming a softening phase which is low in hardness.

Cobalt substantially improves the thermal resistance and abrasion resistance at elevated temperatures and has been established at 6 to 15 percent on the basis of a synergistic effect with the other elements.

In the sintered alloy of the present invention, from a viewpoint of providing the material with a high density and improving the lubricating property, it is very advantageous to impregnate molten lead into the alloy after the alloy is molded and sintered.

In this case, the amount of lead impregnated has been experimentally confirmed to be preferably within the range of 0.05 to 5 percent by weight. Thus, the impregnation of lead into the alloy after sintering contributes to the high density and the lubrication of the sintered material. However, with less than 0.05 percent of lead impregnated, the efiect of the impregnation is not remarkable and the impregnation of more than 5 percent of lead involves a problem in strength from the relation with the density of material before impregnation.

The present invention will be further illustrated by the following Examples by which the present invention is not intended to be limited. All percents are by weight.

EXAMPLE 1 0.7 percent of graphite powder (325 mesh), 0.6 percent (as molybdenum) of a Fe-Mo powder (l50 mesh), 1.5 percent of electrolyzed copper (-150 mesh), 6.5 percent of cobalt powder (l50 mesh) and 1 percent of zinc stearate as a lubricant were added to reduced iron powder mesh) as iron powder, and mixed. The mixture was molded under a pressure of 4.5 ton/cm and sintered at 1,120 to 1,170 C for 30 to 60 minutes in an atmosphere of decomposed ammonium gas. The final composition of the sintered material impregnated with lead was 0.68 percent carbon, 0.57 percent molbydenum, 1.47 percent copper, and 6.44 percent cobalt. The sintered material had a density of 6.8 g/cm and an HRB hardness of 87.

EXAMPLE 2 A sintered material comprising 1.81 percent of carbon, 4.63 percent of molybdenum, 4.65 percent of copper and 14.1 percent of cobalt in the final composition was obtained in the same manner and under the same conditions as described in Example 1. This sintered material had a density of 6.6 g/cm and a HRB hardness of 91.

To examine the abrasion resistance of the sintered alloys obtained in Examples 1 and 2, a hardness test at elevated temperatures and an abrasion test using a valve sheet abrasion testing machine (rotation number 3,000 rpm, spring pressure 35 Kg, valve velocity at the time of valve closing 0.5 m/sec, width of valve 1 mm, number of repeating test 8 X 10 material SUI-I 318) were run. Incidentally, for comparison the same tests were run on a conventionally known cast iron and a sintered ferro alloy. In this case the composition of the cast iron and the ferro alloy are as follows:

SINTERED FERRO ALLOY:

Carbon 1 percent, chromium 3 percent, the balance iron.

CAST IRON:

Carbon 3.02 percent, silicon 2.01 percent, manganese 0.48 percent,

chromium 0.81 percent and the balance iron.

As is shown in FIG. 1, the sintered alloy of the present invention was excellent in its hardness characteristics at elevated temperatures in comparison with the conventional cast iron and sintered ferro alloy. And also, as is shown in FIG. 2, in the abrasion test results,

sition consisting of, in percentages by weight, based on the weight of said composition, from 0.6 to 2 percent carbon, from 0.5 to 5 percent molybdenum, from 6 to 15 percent cobalt, and from 1 to 5 percent copper, the

balance being iron. 

